Drive device, in particular for the locking unit, the injection unit or the ejector of an injection-moulding machine for plastics

Abstract

A drive device which is used in particular for the closing unit, the injection unit or the ejectors of an injection molding machine for plastics and which has a drive element which can be moved axially by an electric motor, and a hydraulic unit which can be moved in the same direction as the drive element by moving the latter. In drive devices for the applications, it is important to first of all perform a rapid regulating movement and then exert high forces. In a known drive device having these features, the hydraulic unit is a hydraulic cylinder which is adjusted by the electric motor via a stroke spindle during the regulating movement and to which pressure medium is fed via a valve for exerting a high force. In this known drive device, in addition to the electrical installation, a complete hydraulic system is also necessary. In addition, high reaction forces act on the stroke spindle. This is avoided wherein the hydraulic unit is a power transmission means having two pistons, which are movable relative to one another and differ from one another in the size of their effective areas, and having an intermediate part which together with the pistons encloses a pressure space filled with a pressure fluid, if the small piston having the smaller effective area is mechanically connected to the drive element, if the hydraulic unit can be moved as an entity for the regulating movement, and if, for exerting a high force by the large piston having the larger effective area, the intermediate part can be locked against displacement relative to a fixed frame.